Q: The Dscam gene in Drosophila can produce 38,016 different protein isoforms due to alternative splicing. If the gene contains 12 alternatives for exon 4, 48 for exon 6, 33 for exon 9, and 2 for exon 17, which equation correctly calculates the number of possible isoforms?

$$38,016 = 12 \times 48 \times 33 \times 2$$

Question 1

Which of the following best describes the outcome of alternative splicing in eukaryotic cells?

Accepted Answer

It increases the number of protein isoforms produced from a single gene.

Question 2

A mutation in an intronic splicing enhancer (ISE) site is most likely to result in which of the following outcomes?

Accepted Answer

Intron retention in the mature mRNA.

Question 3

The Dscam gene in Drosophila can produce 38,016 different protein isoforms due to alternative splicing. If the gene contains 12 alternatives for exon 4, 48 for exon 6, 33 for exon 9, and 2 for exon 17, which equation correctly calculates the number of possible isoforms?

Accepted Answer

$$38,016 = 12 	imes 48 	imes 33 	imes 2$$

Question 4

Which of the following proteins binds to exonic splicing enhancers (ESEs) to promote splicing?

Accepted Answer

SR proteins

Question 5

In the context of spinal muscular atrophy (SMA), what is the molecular consequence of the SMN2 gene mutation affecting the splicing enhancer site?

Accepted Answer

Exon 7 is frequently skipped, resulting in a nonfunctional or less functional SMN protein.

Question 6

Which of the following mechanisms is used by the FDA-approved drug Spinraza (nusinersen) to treat SMA?

Accepted Answer

It blocks an intronic splicing silencer (ISS-N1) to promote inclusion of exon 7 in SMN2 transcripts.

Question 7

Which of the following is a direct effect of phosphorylation as a posttranslational modification?

Accepted Answer

Induction of conformational and functional changes in proteins.

Question 8

Which enzyme is responsible for removing phosphate groups from proteins?

Accepted Answer

Phosphatase

Question 9

What is the role of ubiquitination in posttranslational regulation?

Accepted Answer

It targets proteins for degradation by the proteasome.

Question 10

Which of the following best describes the function of microRNAs (miRNAs) in posttranscriptional regulation?

Accepted Answer

They negatively regulate gene expression by blocking translation or promoting mRNA degradation.

Question 11

A researcher finds that a certain mRNA is rapidly degraded in the cytoplasm. Which sequence element is most likely responsible for this instability?

Accepted Answer

Adenosine–uridine rich element (ARE)

Question 12

Which of the following is a real-world example of RNA interference (RNAi) used as a therapeutic approach?

Accepted Answer

Inclisiran (Leqvio) for lowering LDL cholesterol

Question 13

Which of the following statements about mRNA localization is correct?

Accepted Answer

mRNA localization involves cis-regulatory elements called zip codes that direct mRNA to specific cellular locations.

Question 14

Which of the following best explains why the number of proteins in humans greatly exceeds the number of protein-coding genes?

Accepted Answer

Alternative splicing generates multiple protein isoforms from a single gene.

Question 15

A mutation causes the loss of function of a poly-A binding protein. What is the most likely effect on mRNA?

Accepted Answer

The mRNA will become unstable and be degraded more rapidly.

Question 16

Which of the following is a direct result of phosphorylation of TTP (tristetraprolin) in the regulation of TNFα mRNA?

Accepted Answer

Phosphorylated TTP binds to AREs and stops mRNA degradation.

Question 17

Which of the following best describes the role of the cytoplasmic polyadenylation element (CPE) in mRNA regulation?

Accepted Answer

It allows mRNAs to be stored in a translationally dormant state until activated by phosphorylation.

Question 18

Which of the following is NOT a mechanism of posttranscriptional regulation in eukaryotes?

Accepted Answer

Histone acetylation

Question 19

A patient with spinal muscular atrophy (SMA) is treated with Spinraza. What is the expected molecular effect of this therapy?

Accepted Answer

Increased inclusion of exon 7 in SMN2 mRNA, leading to more functional SMN protein.

Posttranscriptional Regulation in Eukaryotes: Mechanisms and Biological Implications

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